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Posted Mon Oct 3, 2016 8:22 AM
Posted Mon Oct 3, 2016 9:17 AM
jedimatt42, on 03 Oct 2016 - 3:22 PM, said:
I can only imagine it helps save vdp ram by overlapping tables...
That's exactly it as far as I recall. One of the VDP tables overlaps the character definition table, so all the character definitions have been shifted up in the table, so to display the pattern for character "A" you need to print the character ASC("A")+>60 (or whatever the offset is).
Posted Mon Oct 3, 2016 9:48 AM
Posted Mon Oct 3, 2016 10:55 AM
Posted Mon Oct 3, 2016 11:23 AM
Posted Mon Oct 10, 2016 7:37 AM
Both TI Basic and TI Extended Basic have the overlap, but handle it differently. See Thierry's VDP RAM page for a pretty good explanation of this.
Hmm Thierry page does not mention this offset is built into GPL and all the TI BASIC, XB, EA cart, Mini Memory cart, GROM 0 and all other carts that use GPL have this built into them.
It is in the GPL manual and EA Manual also mentions it. Just pointing out a fact that has always existed in GPL even in the TI99 before the TI99/4A.
Posted Sat Feb 3, 2018 5:57 AM
You know I am working on making a XB/EA cart hybrid that just moves the Color table and resets 2 VDP Registers then jumps into EA cart.
I have no idea why the screen bias even exists in TI Basic and XB?
(It does save some VDP memory but not enough to warrant the sacrifice that results.)
Really the Screen Bias creates many more problems than it helps just for a very small amount of VDP space used.
It would make a better XB and faster if the Bias was just not used, so much GPL is used to always deal with this problem.
Not to mention the number of XB programs slowed down and crippled by having to add or minus 96 from every character.
(I think it is one really stupid thing done by Texas Instruments that makes little sense.)
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